In recent years, silicon carbide substrates have been adopted as semiconductor substrates for use in manufacturing semiconductor devices. Silicon carbide has a band gap larger than that of silicon, which has been used more commonly as a material for semiconductor substrates. Hence, a semiconductor device using a silicon carbide substrate advantageously has a large reverse breakdown voltage, low on-resistance, and properties less likely to decrease in a high temperature environment.
In order to efficiently manufacture semiconductor devices, the substrates need to be large in size to some extent. According to U.S. Pat. No. 7,314,520 (Patent Literature 1), a silicon carbide substrate of 76 mm (3 inches) or greater can be manufactured. In the technique described in this specification, a silicon carbide single crystal is grown on a seed crystal by a sublimation method. The seed crystal is required to have a small crystal defect density and a size larger than the size of the silicon carbide substrate to be obtained. However, it is generally difficult to decrease crystal defect density and increase the size of a crystal simultaneously.
Thus, a method using a substrate including a plurality of films each serving as a seed crystal (a seed substrate), instead of using one seed crystal, has been proposed. US Patent Application Publication No. 2004/0187766 (Patent Literature 2) discloses growing a silicon carbide single crystal using a substrate to which a plurality of films are transferred, as a seed substrate.